U.S. patent application number 12/980209 was filed with the patent office on 2011-04-21 for sub volt flash memory system.
Invention is credited to Anh Ly, Hung Q. Nguyen, Sang T. Nguyen, Hieu Van Tran.
Application Number | 20110090743 12/980209 |
Document ID | / |
Family ID | 40252960 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110090743 |
Kind Code |
A1 |
Tran; Hieu Van ; et
al. |
April 21, 2011 |
Sub Volt Flash Memory System
Abstract
Various circuits include MOS transistors that have a bulk
voltage terminal for receiving a bulk voltage that is different
from a supply voltage and ground. The bulk voltage may be
selectively set so that some MOS transistors have a bulk voltage
set to the supply voltage or ground and other MOS transistors have
a bulk voltage that is different. The bulk voltage may be set to
forward or reverse bias pn junctions in the MOS transistor. The
various circuits include comparators, operational amplifiers,
sensing circuits, decoding circuits and the other circuits. The
circuits may be included in a memory system.
Inventors: |
Tran; Hieu Van; (San Jose,
CA) ; Nguyen; Sang T.; (Union City, CA) ; Ly;
Anh; (San Jose, CA) ; Nguyen; Hung Q.;
(Fremont, CA) |
Family ID: |
40252960 |
Appl. No.: |
12/980209 |
Filed: |
December 28, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12623306 |
Nov 20, 2009 |
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12980209 |
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11777895 |
Jul 13, 2007 |
7697365 |
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12623306 |
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Current U.S.
Class: |
365/185.23 |
Current CPC
Class: |
G11C 16/30 20130101;
G11C 16/08 20130101; G11C 16/28 20130101 |
Class at
Publication: |
365/185.23 |
International
Class: |
G11C 16/06 20060101
G11C016/06 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. A method for controlling a memory operation on a flash memory,
the method comprising: applying a preemphasis signal on a signal
line coupled to a plurality of memory cells, the preemphasis signal
having at least one characteristic dependent on loading of the
signal line.
15. The method of claim 14 wherein the preemphasis signal on the
signal line causes at least one of the plurality of memory cells to
perform a memory operation.
16. The method of claim 14 wherein the loading on the signal line
is a resistor-capacitor loading.
17. The method of claim 14 wherein the signal line is a bitline and
the preemphasis signal drives the bitline.
18. The method of claim 14 wherein the signal line is a wordline
and the preemphasis signal drives the wordline.
19. The method of claim 14 wherein the signal line is a
resistance-capacitance (RC) line and the preemphasis signal drives
the RC line.
20. The method of claim 14 wherein the signal line is a
input/output line and the preemphasis signal drives the
input/output line.
21. The method of claim 14 wherein applying a preemphasis signal
includes driving a voltage on the signal line to a negative voltage
level for deselection of at least one of the memory cells.
22. The method of claim 14 wherein applying a preemphasis signal
includes driving a voltage on the signal line that is less than a
forward bias pn junction voltage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/777,895, filed Jul. 13, 2007, the entire contents of which
is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a circuits operating at sub
volt levels, and more particularly, to a memory system operating at
sub volt levels.
BACKGROUND
[0003] Reducing power consumption of electronic devices is
desirable. One approach to reducing power consumption is to reduce
the operating voltages of semiconductor circuits in the electronic
devices. Faster semiconductor circuits are also desirable. Lower
operating voltages may also provide faster circuits. However, lower
operating voltages provide less margins for circuit elements.
SUMMARY
[0004] A system includes MOS transistors that have a bulk voltage
terminal for receiving a bulk voltage that is different from a
supply voltage and ground. The bulk voltage may be selectively set
so that some MOS transistors have a bulk voltage set to the supply
voltage or ground and other MOS transistors have a bulk voltage
that is different. The bulk voltage may be set to forward or
reverse bias pn junctions in the MOS transistor.
[0005] In various aspects, the bulk voltage that is different for
different MOS transistors may be included in comparators,
operational amplifiers, sensing circuits, decoding circuits and the
other circuits in a memory system. In other aspects, the dimensions
of the MOS transistors and the voltages applied thereto may provide
bipolar action in the MOS transistors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1A is a block diagram illustrating an integrated
system-on-chip (SOC) microcontroller memory system consistent with
aspects of the present invention.
[0007] FIG. 1B is a block diagram illustrating a digital multilevel
bit memory system of the SOC microcontroller memory system of FIG.
1A.
[0008] FIG. 2 is a schematic diagram illustrating an embodiment of
an x-decoder of the digital multilevel bit memory system of FIG.
1B.
[0009] FIG. 3A is a schematic diagram illustrating an embodiment of
the x-decoder of the digital multilevel bit memory system of FIG.
1B.
[0010] FIG. 3B is a schematic diagram illustrating an embodiment of
the x-decoder of the digital multilevel bit memory system of FIG.
1B.
[0011] FIG. 3C is a schematic diagram illustrating an embodiment of
the x-decoder of the digital multilevel bit memory system of FIG.
1B.
[0012] FIG. 3D is a schematic diagram illustrating an embodiment of
the x-decoder of the digital multilevel bit memory system of FIG.
1B.
[0013] FIG. 3E is a timing diagram showing waveforms of the
x-decoder of FIG. 3D.
[0014] FIG. 4 is a schematic diagram illustrating a voltage
generator for generating a forward junction current defined
bias.
[0015] FIG. 5 is a graph illustrating the voltage-current
characteristics of a pn junction with defined operating points for
bias voltages of a PMOS transistor.
[0016] FIG. 6 is a schematic diagram illustrating a voltage
generator for generating a tracking under bias voltage.
[0017] FIG. 7 is a schematic diagram illustrating a current
generator as one embodiment of the current generator of FIG. 6.
[0018] FIG. 8 is a schematic diagram illustrating a voltage
generator for generating a tracking over bias voltage.
[0019] FIG. 9 is a schematic diagram illustrating a voltage
generator for generating a tracking over bias voltage based on the
diode voltage.
[0020] FIG. 10 is a schematic diagram illustrating a voltage
generator using a resistor divider to generate the bulk
voltage.
[0021] FIG. 11 is a voltage generator for generating a forward
junction current defined bulk voltage for an NMOS transistor.
[0022] FIG. 12 is a graph illustrating the voltage-current
characteristics of a pn junction with defined operating points for
bias voltages of an NMOS transistor.
[0023] FIG. 13 is a schematic diagram illustrating an x-decoder for
driving the bulk with bipolar action.
[0024] FIG. 14 is a side view and a top plan view of an
illustrative transistor illustrating the parasitic bipolar action
of the x-decoder of FIG. 13.
[0025] FIG. 15 is a side view and top plane view of a layout of a
transistor of the x-decoder of FIG. 13.
[0026] FIG. 16 is a schematic diagram illustrating an x-decoder
with level shifting.
[0027] FIG. 17 is a schematic diagram illustrating a voltage
generator for generating a bulk bias with limited current of the
x-decoder of FIG. 16.
[0028] FIG. 18 is a schematic diagram illustrating a voltage
generator for generating a bias voltage using resistor dividers and
a capacitor divider.
[0029] FIG. 19 is a schematic diagram illustrating a sensing
system.
[0030] FIG. 20 is a schematic diagram illustrating one embodiment
of a differential amplifier of the sensing system of FIG. 19.
[0031] FIG. 21 is a schematic diagram illustrating a first
embodiment of a differential amplifier of the sensing system of
FIG. 19.
[0032] FIG. 22 is a schematic diagram illustrating a second
embodiment of a differential amplifier of the sensing system of
FIG. 19.
[0033] FIG. 23 is a schematic diagram illustrating a third
embodiment of a differential amplifier of the sensing system of
FIG. 19.
[0034] FIG. 24 is a schematic diagram illustrating a bitline
sensing load circuit of the digital multilevel bit memory system of
FIG. 1B.
[0035] FIG. 25 is a schematic diagram illustrating a bitline
sensing load circuit including a load transistor having parasitic
bipolar action of the digital multilevel bit memory system of FIG.
1B.
[0036] FIG. 26 is a schematic diagram illustrating a bitline
sensing load circuit including a switch having parasitic bipolar
action of the digital multilevel bit memory system of FIG. 1B.
[0037] FIG. 27 is a timing diagram showing waveforms with
preemphasis bitline driving in the bitline sensing load circuit of
FIG. 26.
DETAILED DESCRIPTION
[0038] FIG. 1A is a block diagram illustrating an exemplary
integrated system-on-chip (SOC) microcontroller memory system 10
according to the present invention. The SOC microcontroller memory
system 10 includes a digital multilevel bit memory array system
100, a microcontroller 20, and an application resource circuit 30
(e.g., a circuit or block of circuitry that may be devoted to a
particularized application). A system bus includes address, data,
control, and mixed signal bus (which may include digital control,
clock lines, power lines, and analog signal lines). The digital
multilevel bit memory array system 100 is described below in
conjunction with FIG. 1B, serves as a code and data storage for the
system 10. The microcontroller 20 may be, for example, an 8-bit
microcontroller such as industry standard 8051, a RISC core, or a
32 bit ARM controller. The application resource circuit 30 may
include Analog-to-Digital Converters (ADCs) and/or
Digital-to-Analog Converter (DACs), (crystal oscillator) (XTAL),
phase lock loop (PLL), voltage regulators, bandgap reference,
Power-On-Reset (POR) circuit, VDD-detector (for power brown-out
detection, detecting invalid VDD level to avoid invalid chip
operation), TempSensor (temperature sensor to sense chip
temperature), VII-Mon (voltage and current monitor), P-Mon (Power
monitor to monitor chip power consumption) and the like. The
application resource circuit 30 may also include logic elements
(LE) such as CLB (configurable logic block), SLB (spare logic
block), PLA (programmable logic array), ROM table, gate array, and
the like. These mixed logic blocks may be used to provide
additional programmable logic function, such as security protocol
or IO interface protocol control, in addition to those of the
microcontroller 20. In one embodiment, the flash system 100
interfaces with the application resource circuit 30 using the ADC
and DAC to generate high voltage program, erase, and sensing biases
(such as described in U.S. Pat. No. 6,788,608 by Tran et al.), and
using clock signals for charge pumping and for program, erase,
read, and IO burst algorithm control. In another embodiment, the
microcontroller 20 provides security function for the flash system
100 (such as chip password protection, memory sector tag bit, user
ID code, memory block or sector non-volatile or volatile
protection, data encryption and decryption) and error detection and
correction (such as parity check, Hamming code, cyclic codes). In
another embodiment, the microcontroller 20 and application resource
circuit 30 uses the high voltage output (typically 10-20V) of the
charge pump of the flash memory 100 for providing voltage overdrive
for switches and big drivers to reduce impedance.
[0039] FIG. 1B is a block diagram illustrating an exemplary digital
multilevel bit memory array system 100 consistent with one or more
aspects related to the present invention. The digital multilevel
bit memory array system 100 of FIG. 1B comprises a memory array 101
that includes a plurality of memory cells (not shown) and a
reference array 106 that includes a plurality of reference memory
cells (not shown). An N bit digital multilevel cell is defined as a
memory cell capable of storing the 2.sup.N levels. The reference
array 106 is used as a reference system of reference voltage levels
to verify the contents of the memory array 101. In another
embodiment, the memory array 101 may include reference memory cells
for storing the reference voltage levels.
[0040] In one embodiment, the memory array 101 and the reference
array 106 include a drain side injection flash technology, which
uses lower power in hot electron programming, and efficient
injector based Fowler-Nordheim tunneling erasure. The programming
may be done by applying a high voltage on the drain of the memory
cell, a bias voltage on the control gate of the memory cell, and a
bias current on the source of the memory cell. The programming in
effect places electrons on the floating gate of memory cell. The
erase is done by applying a high voltage on the control gate of the
memory cell and a low voltage on the drain and/or source of the
memory cell. The erase in effect removes electrons from the
floating gate of memory cell. The verify (sensing or reading) is
done by placing the memory cell in a voltage mode sensing, e.g., a
bias voltage on the source, a bias voltage on the gate, a bias
current coupled from the source (bitline) to a low bias voltage
such as ground, and the voltage on the source is the readout cell
voltage VCELL. The bias current may be independent of the data
stored in the memory cell. In another embodiment, the verify
(sensing or reading) is done by placing the memory cell in a
current mode sensing, e.g., a low voltage on the source, a bias
voltage on the gate, a load (resistor or transistor) coupled to the
source (bitline) from a high voltage supply, and the voltage on the
load is the readout voltage. In one embodiment, the array
architecture and operating methods may be consistent with those
disclosed in U.S. Pat. No. 6,282,145, entitled "Array Architecture
and Operating Methods for Digital Multilevel Nonvolatile Memory
Integrated Circuit System" by Tran et al., and/or U.S. Pat. No.
7,139,196, entitled "Sub-Volt Sensing For Digital Multilevel
Memory" by Tran, and/or U.S. patent application Ser. No.
11/235,901, U.S. Published Patent Application 2007/0070703 A1,
entitled "Flash Memory Array System including Top Gate Memory Cell"
By Tran et al., which are incorporated herein by reference in their
entirety.
[0041] The multilevel memory cells of the memory array 101 may be
arranged in various ways, such as in rows and columns or in
segments. Various addressing schemes may be used which organize the
memory cells into bytes, pages or other arrangements.
[0042] The digital multilevel bit memory array system 100 further
includes an x-decoder 120, a y-decoder 110, an address controller
162, a sense amplifier circuit 111, and an intelligent input/output
interface 196. The y-decoder 110 controls bitlines (not shown)
coupled to columns in memory cells and the reference voltage cells,
during a write, read (or verify), and erase operations. The sense
amplifier 111 senses the read data which is provided to the I/O
interface 196. The I/O interface 196 also buffers input into the
memory array system 100. The sense amplifier 111 also senses the
read data and verifies the read data against input data during
memory programming or erasing.
[0043] In response to address and other control signals, the
address controller 162 decodes the address signal and controls
page, byte, segment or other addressing for the x-decoder 120 and
the y-decoder 110. The x-decoder 120 selects a row or a block of
rows in the arrays 101 and 106 based on the signals from the
address controller 162 and provides precise multilevel bias values
over temperature, process, and power supply used for consistent
single level or multilevel memory operation for the memory array
101.
[0044] The system 100 includes a logic controller 163 to control
various chip functionality and to interface with the application
resource circuit 30 and the microcontroller 20.
[0045] The system 100 includes a voltage/current generator
(V&I-GEN) 175 to generate biases for program, erase and read
operations. The V&I-GEN 175 may interface with the application
resource circuit 30, for example, by using the ADC and DAC for
biases and pulse-shape generation and the phase lock loop and the
crystal oscillator for clock sources.
[0046] The system 100 includes a flash built-in self test (FBIST)
181 that is used to test on-chip non-volatile program and erase
function, redundancy self repair, addressing uniqueness, defect
open/short screening for bitline, wordline or sourceline, memory
cell terminal leakage test (such as bitline, wordline or
sourceline), power consumption test (standby or active), disturb
screening, infant mortality screening, margin screening, at-speed
test, and the like.
[0047] The system 100 further includes power related circuits (not
shown), such as band gap voltage generators, charge pumps, voltage
regulators, and power management systems, and other control
circuits (not shown) such as voltage algorithm controllers.
[0048] The system 100 may execute various operations on the memory
array 101. An erase operation may be done to erase all selected
multilevel cells by removing the charge on selected memory cells
according to the operating requirements of the non-volatile memory
technology used. A data load operation may be used to load in a
plurality of bytes of data to be programmed into the memory cells,
e.g., 0 to 512 bytes in a page. A read operation may be done to
read out in parallel a plurality of bytes of data if the data
(digital bits), e.g., 512 bytes within a page, stored in the
multilevel cells. A program operation may be done to store in
parallel a plurality of bytes of data in (digital bits) into the
multilevel cells by placing an appropriate charge on selected
multilevel cells depending on the operating requirements of the
non-volatile memory technology used. The operations on the memory
may be, for example, consistent with the operations described in
U.S. Pat. No. 6,282,145, incorporated herein by reference
above.
[0049] FIG. 2 is a schematic diagram illustrating one embodiment of
the x-decoder 120 of the multilevel bit memory system 100. The
x-decoder 120 comprises a pre-decoder 202, a plurality of decoders
204-0 through 204-7, and a plurality of word line drivers 206-0
through 206-7. As an exemplary embodiment, eight decoders 204 and
eight word line drivers 206 are shown; however, any number of
decoders 204 and word line drivers 206 may be used. The pre-decoder
202 decodes a plurality of address signals, such as address signals
XPA, XPB and XPC, for enabling selected ones of the decoders 204.
In one embodiment, the pre-decoder 202 comprises a NAND gate 211
and an inverter 212. The decoders 204 provide an enable signal to a
corresponding word line driver 206 in response to an enable signal
from the pre-decoder 202 and a corresponding bit line select signal
251-0 through 251-7. In one embodiment, the decoder 204 comprises
PMOS transistors 221 and 223 and an NMOS transistor 222. (For
clarity, only decoder 204-0 shows the reference numerals of the
transistors therein.) The plurality of word line drivers 206-0
through 206-7 provides a drive signal on a word line WL0 through
WL7, respectively. In one embodiment, the word line driver 206
comprises a PMOS transistor 231 and an NMOS transistor 232. (For
clarity, only word line driver 206-0 shows the reference numerals
of the transistors.)
[0050] The bulks of the PMOS transistors 221, 223 and 231 are
coupled to the supply voltage VDD. The bulks of the NMOS
transistors 222 and 232 are coupled to ground.
[0051] FIG. 3 is a schematic diagram illustrating another
embodiment of the x-decoder 120 multilevel bit memory system 100.
The x-decoder 120 comprises a pre-decoder 302, a plurality of
decoders 304-0 through 304-7, and a plurality of word line drivers
306-0 through 306-7. The pre-decoder 302 decodes a plurality of
address signals, such as address signals XPA, XPB and XPC for
enabling selected ones of the decoders 304. In one embodiment, the
pre-decoder 302 comprises a NAND gate 311 and an inverter 312. The
decoders 304 provide an enable signal to a corresponding word line
driver 306 in response to an enable signal from the pre-decoder 302
and a corresponding bit line select signal 351-0 through 351-7. In
one embodiment, the decoder 304 comprises PMOS transistors 321 and
323 and an NMOS transistor 322. (For clarity, only decoder 304-0
shows the reference numerals of the transistors.) The plurality of
word line drivers 306-0 through 306-7 provides a drive signal on a
word line WL0 through WL7, respectively. In one embodiment, the
word line driver 306 comprises a PMOS transistor 331 and an NMOS
transistor 332. (For clarity, only word line driver 306-0 shows the
reference numerals of the transistors.)
[0052] The PMOS transistors 321, 323, and 331 include bulk voltage
terminals 361, 363, and 371, respectively, for coupling to a power
source that supplies corresponding bulk voltages that may be
different from the supply voltage Vdd. The power source may be
selected from the voltage generators 400, 800, 900, and 1000, which
are described below in conjunction with FIGS. 4, 8, 9, and 10,
respectively. The bulk voltage terminal 361, 363, and 371 may
receive voltages that are different from each other, the same, or
combinations thereof. The bulk voltage applied to the bulk voltage
terminals 361, 363, 371 may be set at a level to bias the pn
junctions in the PMOS transistors to set the operating current and
voltage of the pn junction at a level above or below the junction
voltage. In a similar manner, the NMOS transistors 322 and 332
include bulk voltage terminals 362 and 372, respectively, for
coupling to a voltage supply that may be different than ground. The
bulk voltage terminals 322 and 332 may receive voltages that are
different from each other, the same, or combinations thereof. In
one embodiment, the bulk voltages are set at a voltage level other
than the supply voltage Vdd or ground only for the transistors in
the selected decoder 304 and corresponding word line driver 306.
The selective setting of bulk voltages provides tracking bias body
driving of the transistors in the selected decoder 304 and
corresponding word line driver 306. The selective setting of bulk
voltages is done individually for one wordline driver 306, for
example for selected wordline driver 306-0, or for all 8 wordline
drivers 306-0 to 306-7 (i.e., one sector is selected, and one
sector includes all 8 wordlines) even though only one out of 8
wordline drivers 306 in a sector is selected, The selective setting
of bulk voltages reduces power consumption of the system 100 in
view of providing the bulk voltages to all decoders 304 and word
line drivers 306. The tracking bias also reduces noise and reduces
likelihood of latch up. The selective setting of bulk voltages can
be done automatically by the circuit that uses a bulk voltage for
self optimization (to be called self conscious circuitry). Thus,
circuit selects its own bulk voltage, for example either less than
the pn forward junction voltage for a goal of less noises, or
slightly larger than the pn forward junction voltage for a goal of
maximum speed.
[0053] FIG. 4 is a schematic diagram illustrating a voltage
generator 400 for generating a forward junction current defined
bias for the bulk voltage. The voltage generator 400 may be part of
the V&I-GEN 175 (FIG. 1A). The voltage generator 400 comprises
a reverse diode-connected PMOS transistor 401 coupled between a
supply voltage Vdd and a bias voltage terminal 403, and further
comprises a current source 402 coupled between the drain of the
PMOS transistor 401 and ground. The bias voltage terminal 403 is
coupled to the drain of the PMOS transistor 401. The gate of the
PMOS transistor 401 is coupled to the supply voltage Vdd. The
source of the PMOS transistor 401 is coupled to the supply voltage
Vdd. The bulk of the PMOS transistor 401 is coupled to the bias
voltage terminal 403. By way of illustration, the physical layout
of the PMOS transistor 401 is shown with an n-well 410 and
p-regions 411-1 and 411-2, which may form a source and drain. The
current source 402 flows through the terminal 403, through the bulk
of the PMOS transistor 401 and into the source of the PMOS
transistor 401. The source of the PMOS transistor 401 and the bulk
of the PMOS transistor 401 constitute a pn junction, through which
the current from the current source 402 flows. In one embodiment
the physical effect tracking is done by using the PMOS 401 as an
exact replica to the PMOS transistors to which the bulk voltage is
provided. This is similarly done for other tracking bias
generators, such as the generators of FIGS. 7 and 11.
[0054] FIG. 5 is a graph illustrating the voltage-current
characteristics of a pn junction as indicated by a line 501 with
defined operating points for bias voltages of a PMOS transistor.
The voltage generator 400 operates at an operating point 510 that
is above the threshold voltage (VDIO) of the pn junction formed by
the p-regions 411 and the n-well 410. The operating point 510 is
selected at a level to avoid noise and potential latch-up that
occurs at higher voltages and currents. At high current,
substantial substrate current may be injected into the substrate
and could potentially turn on a parasitic PNP transistor formed of
a source junction of the PMOS (P+ source), a bulk of the PMOS (N
from N-well) and silicon substrate P-sub. This in turn potentially
turns on an adjacent parasitic NPN transistor formed of a N+
drain/source of an adjacent NMOS transistor, the silicon substrate
P-sub, and the N-well of the PMOS transistor. These two bipolar
transistors are coupled in a positive feedback action which may
cause a latch-up condition to happen, and thus a very high current
is introduced by these two bipolar devices and it could cause
destructive device failure. Noise is induced by the injected
substrate current since this current could be picked up
inadvertently. Also this current could modulate the substrate
potential locally.
[0055] FIG. 6 is a schematic diagram illustrating a voltage
generator 600 for generating a tracking under bias voltage. The
voltage generator 600 may be part of the V&I-GEN 175 (FIG. 1A).
The voltage generator comprises a resistor 601 and a current
generator 602 coupled in series between a supply voltage Vdd and
ground and forming a common node between the resistor 601 (having a
resistance R601) and the current generator 602 that is coupled to a
bulk voltage terminal 603. The voltage generator 600 generates a
bulk voltage VXB applied to the bulk voltage terminal 603 that
operates at an operating point 520 (FIG. 5). The voltage dVXB
(voltage across the resistor 601 (R601)) is generated based on a
ratio of resistances (R1 and R601) of resistor 601 and a reference
resistor R1, such as a resistor 709 in FIG. 7. In one embodiment,
the voltage dVXB is set at 0.8 of the pn junction voltage VDIO. The
voltage generator 600 operates at the operating 520 that has less
noise than the operating point 510 but has less than an optimal
tracking bias.
[0056] FIG. 7 is a schematic diagram illustrating a current
generator 700, which may be one embodiment of the current generator
602. The current generator 700 comprises a plurality of PMOS
transistors 701, 702 and 703, a plurality of NMOS transistors 704
and 705, and a resistor 709 (having a resistance R1). The
transistors 701, 703, and 704 are arranged to provide a current
that is mirrored through the resistor 709 from the current mirror
formed of the transistors 702 and 701 and current mirror of the
transistor 704 and 705. The current through the resistor 709 equals
the diode voltage VDIO divided by the resistance of the resistor
709, or I=VDIO/R1. By way of illustration, the physical layout of
the PMOS transistor 703 is shown with an n-well 710 and p-regions
711-1 and 711-2, which may form a source and drain.
[0057] FIG. 8 is a schematic diagram illustrating a voltage
generator 800 for generating a tracking over bias voltage VXB. The
voltage generator 800 may be part of the V&I-GEN 175 (FIG. 1A).
The voltage generator 800 comprises an over-biasing resistor 801
and a current source 802 that is coupled in series between a supply
voltage Vdd and ground and forming a common node between the
resistor 801 and the current source 802 that is coupled to a bulk
voltage terminal 803. The current of the current source 802 is
selected to provide a tracking bias voltage approximately equal to
the pn junction voltage plus a difference voltage (dV) to set an
operating point between the operating point 510 and an operating
point 530 (FIG. 5).
[0058] FIG. 9 is a schematic diagram illustrating a voltage
generator 900 for generating a tracking over bias voltage based on
the diode voltage. The voltage generator 900 may be part of the
V&I-GEN 175 (FIG. 1A). The voltage generator 900 comprises a
resistor 901 (having a resistance R901) and a current source 902
arranged in a similar manner as the resistor 801 and current source
802 (FIG. 8) to form a bulk voltage terminal 903 that provides a
tracking bias bulk voltage based on a ratio of the pn junction
voltage VDIO. The current of the current source 902 is selected as
a current that is the ratio of the pn junction voltage VDIO and
resistance of a resistor R1. The voltage dVXB is based on a ratio
of resistances (R1 and R901) and VDIO. Refer again to FIG. 5, the
voltage generator 900 generates a tracking bias bulk voltage to
operate at an operating point 530 to set the voltage and
current.
[0059] FIG. 10 is a schematic diagram illustrating a voltage
generator 1000 using a resistor divider to generate the bulk
voltage. The voltage generator 1000 may be part of the V&I-GEN
175 (FIG. 1A). The voltage generator 1000 comprises a plurality of
resistors 1001 and 1002 coupled in a series between the supply
voltage Vdd and ground and form a common node to provide a divided
voltage on a bulk voltage terminal 1003. The resistance of the
resistors 1001 and 1002 are selected to provide a bias voltage dVXB
(VXB=Vdd-dVXB) approximately equal to the pn junction voltage VDIO
minus a difference voltage (dV) to set an operating point between
the operating point 510 and an operating point 530 (FIG. 5).
[0060] FIG. 11 is a voltage generator 1100 for generating a forward
junction current defined bulk voltage for an NMOS transistor. The
voltage generator 1100 may be part of the V&I-GEN 175 (FIG.
1A). The voltage generator 1100 comprises a current source 1102
coupled between a supply voltage Vdd and a bias voltage terminal
1103, and further comprises a diode connected NMOS transistor 1101
coupled between the bias voltage terminal 1102 and ground. The bulk
of the NMOS transistor 1101 is coupled to the bias voltage terminal
1103. By way of illustration, the physical layout of the NMOS
transistor 1101 is shown with a p-well 1110 and n-regions 1111-1
and 1111-2, which may form a source and drain.
[0061] FIG. 12 is a graph illustrating the voltage-current
characteristics of a pn junction as indicated by a line 1201 with a
defined operating point for bias voltages of the NMOS transistor
1101. The voltage generator 1100 operates at an operating point
1210 that is above the threshold voltage (VDIO) of the pn junction
formed by the n-regions 1111 and the p-well 1110. The operating
point 1210 is selected at a level to avoid noise and potential
latch-up that occurs at higher voltages and currents.
[0062] FIG. 3B is a schematic diagram illustrating an x-decoder
2800, which is one embodiment of the x-decoder 120. The x-decoder
2800 comprises a pre-decoder 302, a plurality of decoders 304-0
through 304-7, and a plurality of word line drivers 306-0 through
306-7 arranged in a similar manner as the x-decoder of FIG. 3A. The
x-decoder 2800 further comprises a bulk voltage generator 2807 for
providing a bulk voltage on the bulk voltage terminals 361 of the
decoders 304 and on the bulk voltage terminals 371 of the word line
drivers 306. The bulk voltage generator 2807 comprises a plurality
of PMOS transistors 2871 and 2873. The PMOS transistor 2871 is
coupled between a voltage node 2872 and a common node formed of the
drain of the transistor 2871 and drain of the PMOS transistor 2873.
This common node is coupled to the bulk voltage terminals 361 and
371. The bulk of the PMOS transistors 2871 and 2873 are coupled to
a voltage node 2874. The gate of the PMOS transistor 2871 is
enabled by an enable signal from the predecoder 302 (output of the
NAND gate 311 of the predecoder 302). The gate of the PMOS
transistor 2873 is enabled by an enable signal from the predecoder
302 (output of the inverter 312 of the predecoder 302) When
enabled, the PMOS transistor 2871 pulls up the voltage on the bulk
voltage terminals 361 and 371 to the voltage on the voltage node
2872, which may be, for example, the supply voltage Vdd. When the
PMOS transistor 2871 is disabled, the PMOS transistor 2873 pulls up
the voltage on the bulk voltage terminals 361 and 371 to the
voltage (which may be the same, higher or lower than VDD) on the
voltage node 2874, which may be, controlled to reverse or forward
bias pn junctions of the PMOS transistors 321 and 331. In the case
that the voltage on the voltage node 2874 is higher than the supply
voltage Vdd, the bulks of the transistor 2871 and 2873 may be
re-connected or switched by a multiplexer (not shown) to the node
2874.
[0063] FIG. 3C is a schematic diagram illustrating an embodiment of
the x-decoder 2900, which is one embodiment of the x-decoder 120.
The x-decoder 2900 comprises a pre-decoder 302, a plurality of
decoders 304-0 through 304-7, and a plurality of word line drivers
306-0 through 306-7 arranged in a similar manner as the x-decoder
of FIG. 3A. The x-decoder 2900 further comprises a plurality of
bulk voltage generators 2907-0 through 2907-7 for providing a bulk
voltage on the bulk voltage terminals 361 of the respective
decoders 304-0 through 304-7 and on the bulk voltage terminals 371
of the respective word line drivers 306-0 through 306-7. The bulk
voltage generator 2907 comprises a plurality of PMOS transistors
2971 and 2973. The PMOS transistor 2971 is coupled between a
voltage node 2972 and a common node formed of the drains of the
PMOS transistor 2973 and the PMOS transistor 2971 and the bulk
voltage terminals 361 and 371. The bulk of the PMOS transistors
2971 and 2973 are coupled to a voltage node 2972. The gate of the
PMOS transistor 2971 is enabled by an enable signal from the drain
of the transistor 321. When enabled, the PMOS transistor 2971 pulls
up the voltage on the bulk voltage terminals 361 and 371 to the
voltage on the voltage node 2972, which may be, for example, the
supply voltage Vdd. When the PMOS transistor 2971 is disabled, and
the PMOS transistor 2973 is enabled by the output of the word line
driver 306, the PMOS transistor 2973 pulls up the voltage (which
may be the same, higher or lower than VDD) on the bulk voltage
terminals 361 and 371 to the voltage on the voltage node 2974,
which may be, controlled to reverse or forward bias pn junctions of
the PMOS transistors 321 and 331. In the case that the voltage on
the voltage node 2974 is higher than the supply voltage Vdd, the
bulks of the transistor 2971 and 2973 may be re-connected or
switched by a multiplexer (not shown) to the node 2974.
[0064] FIG. 3D is a schematic diagram illustrating an x-decoder
3000, which is one embodiment of the x-decoder 120. The x-decoder
3000 comprises a pre-decoder 302, a plurality of decoders 304-0
through 304-7, and a plurality of bulk voltage generators 2907-0
through 2907-7 arranged in a similar manner as the x-decoder 2900
of FIG. 3C. The x-decoder 3000 further comprises a plurality of
word line drivers 3006-0 through 3006-7 that provide a drive signal
on a word line WL0 through WL7, respectively. In one embodiment,
the word line driver 306 comprises a PMOS transistor 3031 and an
NMOS transistor 3032. (For clarity, only word line driver 3006-0
shows the reference numerals of the transistors.) The sources of
the NMOS transistors 3032 are coupled to a virtual ground (VGND)
terminal 3004. The x-decoder 3000 further comprises a virtual
ground selection circuit 3001 that selectively couples the virtual
ground terminal 3004 to ground or to a virtual negative voltage
(VGNDSUP) terminal 3005. The virtual ground selection circuit 3001
comprises a plurality of NMOS transistors 3002 and 3003 coupled in
series between the virtual negative voltage (VGNDSUP) terminal 3005
and ground. The NMOS transistors 3002 and 3003 are enabled by the
output of the NAND gate 311 and the inverter 312, respectively, to
pull up or pull down the voltage on the terminal 3304 to either a
virtual negative voltage or ground, respectively.
[0065] The virtual ground level (vGND) is a negative level, e.g.,
-0.6 to -0.05V, to deselect the unselected wordlines locally and
selectively, for example deselecting 7 unselected wordlines out of
8 wordlines in a sector. This is to avoid the neighboring cells
from interfering with the operation of the selected cell such as
reducing the adjacent leakage in programming in a sector. Or
reducing the operation of the selected cell from interfering the
unselected cell such as the program disturb. The virtual ground
level (vGND) value may be chosen to avoid forward biasing the
Psub/N+ source/drain regions of an NMOS transistor in a Psub CMOS
process, hence chosen as an underbias ratio .alpha. of the pn
junction voltage VDIO.
[0066] For example=.alpha.*VDIO=-0.5*0.6=-0.3V
[0067] The negative level is for example generated by switching a
predetermined-value capacitor (not shown) from a high bias level to
a low bias level and the capacitor being coupled to the terminal
(vGNDSUP) 3005. In one embodiment, the vGND negative level can be
used to locally and selectively deselect the bitline decoders
(Y-muxing) to reduce the leakage current on the selected
bitline.
[0068] FIG. 3E is a timing diagram showing waveforms of the
x-decoder 3000. A waveform 2892 is the ideal voltage on the word
line during a transition. A waveform 2895 is the voltage on the
word line with `normal` RC behavior with a rise time (t-WLRC) from
the RC time constant of the word line. A waveform 2893 is the
voltage on the word line with selective bulk decoding. The waveform
2893 has a rise time (t-WLRCn) from the selective decoding of
enabling one decoder and providing a virtual ground level, shown as
waveform 2896. Waveforms 2896 and 2897 are the voltages of the
virtual ground (vGND) and the bulk voltage (VXB), respectively.
[0069] FIG. 13 is a schematic diagram illustrating an x-decoder 120
for driving the bulk with bipolar action in parallel with the MOS
transistor action. The x-decoder 120 comprises a pre-decoder 302, a
plurality of decoders 304, and a plurality of word line drivers
1306. The pre-decoder 302 and the decoders 304 are described above
in conjunction with FIG. 3. The word line driver 1306 comprises a
PMOS transistor 1331 and a NMOS transistor 1332 arranged in a
similar manner as the respective PMOS transistor 331 and NMOS
transistor 332 of the word line driver 306 (FIG. 3). (For clarity,
only word line driver 1306-0 shows the reference numerals of the
transistors.) The word line driver 1306 further comprises an
effective PNP transistor 1333 formed by parasitic bipolar action in
the p and n regions of the PMOS transistor 1331 on a bulk voltage
terminal 1371. The bipolar effect may occur effectively as
dimensions of the PMOS transistor 1331 are small relative to the
depletion regions that form as a PNP transistor. In effect the PNP
is a lateral PNP with the base region defined by the channel length
of the PMOS that acts effectively with fast base transit time
across the small base region. As the dimensions of the PMOS
transistor 1331 decrease, the PMOS transistor 1331 operates as if
it includes an effective lateral PNP transistor 1333 coupled
thereto in parallel. In one embodiment, the decoder 304 includes
bipolar action.
[0070] FIG. 14 is a side view and a top plan view of an
illustrative transistor illustrating the parasitic bipolar action
of the word line driver 1306. The transistor comprises an n well
1401, a plurality of n doped regions 1402-1 and 1402-2, a plurality
of p doped regions 1403-1 and 1403-2, and a gate 1404. A PNP
transistor 1433 is shown including a collector coupled to the p
doped regions 1403-2, an emitter coupled to the p doped region
1403-1, and a base coupled to the n doped region 1402-2. The p
doped regions 1403-1 and 1403-2 and the gate 1404 have rectangular
shapes.
[0071] FIG. 15 is a side view and top plan view of a layout of a
transistor in the word line decoders 1306. The transistor comprises
an n well 1501, a plurality of n doped regions 1502-1 and 1502-2, a
plurality of p doped regions 1503-1 and 1503-2, and a plurality of
gates 1504. The p doped region 1503-1 is rectangular. The p doped
region 1503-2 has a rectangularized annular shape. Since for the
parasitic lateral PNP, the collector region (p doped region 1503-2)
now is extended to completely surround the whole emitter region (p
doped region 1503-1), the PNP is more effective.
[0072] FIG. 16 is a schematic diagram illustrating an x-decoder
1600 with level shifting. In one embodiment, the x-decoder 1600 is
used for circuits having a limited current supply from an on-chip
word line charge pump. The x-decoder 1600 comprises a level shift
circuit 1602 and a drive circuit 1606. The level shift circuit 1602
shifts the voltage above the supply voltage Vdd to another level,
for example, a higher voltage VPWL on a line 1609, to provide a
decode signal 1608 operating at a higher voltage than the supply
voltage Vdd. The level shift circuit 1602 comprises a plurality of
PMOS transistors 1610 and 1611, a plurality of NMOS transistors
1612 and 1613, and a plurality of inverters 1614 and 1615. The
transistors 1610, 1611, 1612 and 1613 are cross-coupled and
selectively controlled by the NMOS transistors 1612 and 1613 in
response to a control signal 1617 applied through the inverter 1614
and 1615, respectively. The drive circuit 1606 comprises a PMOS
transistor 1631 and an NMOS transistor 1632. The bulk of the PMOS
transistor 1631 is coupled to a bulk voltage terminal 1603 for
receiving a selective bulk voltage, such as described above in
conjunction with FIGS. 3-15. In one embodiment, the x-decoder 1600
includes bipolar action on the PMOS transistors.
[0073] FIG. 17 is a schematic diagram illustrating a voltage
generator 1700 for generating a bulk bias with limited current for
the bulk voltage terminal 1603. The voltage generator 1700 may be
part of the V&I-GEN 175 (FIG. 1A). The voltage generator 1700
comprises a plurality of PMOS transistors 1701 and 1702, a
plurality of current sources 1703 and 1704, and a resistor 1705.
The resistor 1705, the PMOS transistor 1701, and the current source
1703 are coupled in series to control a current that is mirrored in
the PMOS transistor 1702 with the current source 1704. The PMOS
transistor 1702 includes a source coupled to a bulk voltage
terminal 1707 to provide the bias voltage of the level shift on the
bulk voltage terminal 1603 (FIG. 16).
[0074] FIG. 18 is a schematic diagram illustrating a voltage
generator 1800 for generating a bias voltage using resistor
dividers and a capacitor divider. The voltage generator 1800 may be
part of the V&I-GEN 175 (FIG. 1A). The voltage generator 1800
comprises a plurality of resistors 1801, 1802, 1803, and 1804, a
plurality of capacitors 1805 and 1806, and a switch 1807. The
resistors 1801 and 1802 are coupled in series to form a voltage
divider, with a divided voltage applied to one terminal of the
switch 1807. The resistors 1803 and 1804 are formed as a voltage
divider to provide a voltage on a bulk voltage terminal 1808. The
capacitors 1805 and 1806 are coupled in series to form a capacitor
divider to apply the divided voltage to the bulk voltage terminal
1808. The capacitor divider may provide a faster circuit for higher
frequency signals. The switch 1807 is used for sampling at
predetermined time intervals the low impedance branch formed of the
resistors 1801 and 1802 onto the bulk voltage terminal 1808.
[0075] FIG. 19 is a schematic diagram illustrating a sensing system
1900. The sensing system 1900 comprises a reference column 1901, a
plurality of data columns 1902-0 through 1902-N, and a plurality of
comparators 1903-0 through 1903-N. The reference column 1901
comprises a reference memory cell 1911, an NMOS transistor 1912,
and a PMOS transistor 1915. A bitline resistor 1913 is shown to
indicate resistance on the bitline. A bitline capacitor 1914 is
shown to indicate capacitance on the bitline. The reference column
1901 provides a voltage reference on a reference line 1904 which is
applied to a first input of each of the comparators 1903-0 through
1903-N. Each data column 1902 comprises a data memory cell 1921, an
NMOS transistor 1922 and a PMOS transistor 1925. A bitline resistor
1923 is shown to indicate resistance on the bitline. A bitline
capacitor 1924 is shown to indicate capacitance on the bitline.
Each of the data columns 1902-0 through 1902-N provides a data
output voltage to a second input of a respective comparator 1903-0
through 1903-N so that the comparator 1903 provides an output
indicative of the stored data in the corresponding data column
1902. The differential amplifier 1903 may be one of the
differential amplifiers of FIGS. 20-23.
[0076] FIG. 20 is a schematic diagram illustrating a differential
amplifier 2000. The differential amplifier 2000 comprises a
plurality of PMOS transistors 2001 and 2002 and a plurality of NMOS
transistors 2014, 2015 and 2016 arranged as a differential
amplifier with differential pair input terminals coupled to the
gates of the NMOS transistors 2014 and 2015. The gate of the NMOS
transistor 2016 receives a bias signal. The differential amplifier
2000 further comprises a PMOS transistor 2003 and an NMOS
transistor 2017 arranged as an output buffer stage. The gate of the
NMOS transistor 2017 receives a bias signal. The bulks of the PMOS
transistors 2001, 2002, and 2003 are coupled to the supply voltage
Vdd.
[0077] FIG. 21 is a schematic diagram illustrating a differential
amplifier 2100. The differential amplifier 2100 comprises a
plurality of PMOS transistors 2101 and 2102 and a plurality of NMOS
transistors 2114, 2115 and 2116 arranged as a differential
amplifier with differential pair input terminals coupled to the
gates of the NMOS transistors 2114 and 2115. The gate of the NMOS
transistor 2116 receives a bias signal. The bulk of the PMOS
transistors 2101 and 2102 are coupled to a bulk voltage terminal
2110. The differential amplifier 2100 further comprises a PMOS
transistor 2103 and an NMOS transistor 2117 arranged as an output
buffer stage. The gate of the NMOS transistor 2117 receives a bias
signal. The bulk of the PMOS transistor 2103 is coupled to a bulk
voltage terminal 2111. The bulk voltage terminals 2110 and 2111 may
receive voltages that are different from each other or the
same.
[0078] FIG. 22 is a schematic diagram illustrating a differential
amplifier 2200. The differential amplifier 2200 comprises a
plurality of PMOS transistors 2201 and 2202 and a plurality of NMOS
transistors 2214, 2215 and 2216 arranged as a differential
amplifier with differential pair input terminals coupled to the
gates of the NMOS transistors 2214 and 2215. The gate of the NMOS
transistor 2216 receives a bias signal. The differential amplifier
2200 further comprises a PMOS transistor 2203 and an NMOS
transistor 2217 arranged as an output buffer stage. The gate of the
NMOS transistor 2217 receives a bias signal. The bulk of the PMOS
transistor 2203 is coupled to a bulk voltage terminal 2211. The
differential amplifier 2200 further comprises a tracking p-region
load body bias circuit formed of a reverse diode connected PMOS
transistor 2204 and an NMOS transistor 2218, which has a gate that
receives a bias signal. The drain of the diode connected PMOS
transistor 2204 is coupled to the bulk of the PMOS transistors
2201, 2202, and 2204 to provide local self-tracking biasing of the
bulk of the transistors 2201, 2202 and 2204. In one embodiment, the
transistor 2204 is an exact replica or substantially exact replica
of the transistors 2201 and 2202 in terms of dimension and layout
structure. The physical location of the transistor 2204 may be
between or close to the transistors 2201 and 2202.
[0079] FIG. 23 is a schematic diagram illustrating a differential
amplifier 2300. The differential amplifier 2300 comprises a
plurality of PMOS transistors 2301 and 2302 and a plurality of NMOS
transistors 2314, 2315 and 2316 arranged as a differential
amplifier with differential pair input terminals coupled to the
gates of the NMOS transistors 2314 and 2315. The gate of the NMOS
transistor 2316 receives a bias signal. The differential amplifier
2300 further comprises a PMOS transistor 2303 and an NMOS
transistor 2317 arranged as an output buffer stage. The gate of the
NMOS transistor 2317 receives a bias signal. The differential
amplifier 2300 further comprises an adaptive tracking circuit 2310
that provides n-pair body bias of the NMOS transistors 2314 and
2315. The tracking circuit 3210 provides an output bias that is a
determined function of the input voltage (VINN). The transistors
2316 and 2317 may receive another bulk bias voltage. The tracking
circuit 3210 comprises a loading circuit 2319 and an NMOS
transistor 2318 that provides a bulk voltage on the bulk of the
NMOS transistors 2314 and 2315. The gate of the NMOS transistor
2314 is biased by the input signal DINN, which is also applied to
the gate of the NMOS transistor 2318.
[0080] FIG. 24 is a schematic diagram illustrating a bitline
sensing load circuit 2400. The bitline sensing load circuit 2400
comprises a memory cell 2411 and an NMOS transistor 2412, and a
PMOS transistor 2415. A bitline resistor 2413 is shown to indicate
resistance on the bitline. A bitline capacitor 2414 is shown to
indicate capacitance on the bitline. The bulk of the PMOS
transistor 2415 is coupled to a bulk voltage terminal 2403 for
receiving a voltage that may be different from the supply voltage
or the same. The bulk voltage may be set as described above in
conjunction with FIG. 3. In one embodiment, the bulk voltage is
less than the voltage supply Vdd. In another embodiment, the bulk
voltage is a bias voltage tracking forward pn diode voltage. The
drain of the PMOS transistor 2415 is coupled to a bitline 2416.
[0081] FIG. 25 is a schematic diagram illustrating a bitline
sensing load circuit 2500 including a load transistor having
parasitic bipolar action. The bitline sensing load circuit 2500
comprises a memory cell 2511, an NMOS transistor 2512, and a PMOS
transistor 2515. A bitline resistor 2513 is shown to indicate
resistance on the bitline. A bitline capacitor 2514 is shown to
indicate capacitance on the bitline. The drain of the PMOS
transistor 2503 is coupled to a bitline 2516. An npn transistor
2515 is representative of an effective parasitic bipolar action on
the NMOS transistor 2512 if the dimensions of the NMOS transistor
2512 are sufficiently small or the voltages applied thereto are
sufficiently large, or a combination thereof, in a similar manner
as the bipolar parasitic action described above.
[0082] FIG. 26 is a schematic diagram illustrating a bitline
sensing load circuit 2600 including a switch having parasitic
bipolar action. The bitline sensing load circuit 2600 comprises a
memory cell 2611, an NMOS transistor 2612, and a PMOS transistor
2615. A bitline resistor 2613 is shown to indicate resistance on
the bitline. A bitline capacitor 2614 is shown to indicate
capacitance on the bitline. The drain of the PMOS transistor 2603
is coupled to a bitline 2616. The bitline sensing load circuit 2600
further comprises an npn transistor 2615 that is used for
predriving or providing preemphasis driving on the bitline by
switching the collector of the transistor 2615 to be selectively
coupled to the bitline 2616. FIG. 27 is a timing diagram showing
waveforms with preemphasis bitline driving in the bitline sensing
load circuit 2600. A predetermined voltage dV1 is overdriven over
the final level V1 for a predetermined period t1 over t-RC to
achieve preemphasis. A waveform 2701 having an overshoot dV1 and a
pulse width t1 is substantially at the beginning of the bitline for
driving with preemphasis. A waveform 2702 rising to V1 is
substantially at the beginning of the bitline for driving without
preemphasis. Waveforms 2703 and 2705 show `preemphasis behavior`
and `normal RC behavior`, respectively, substantially at the end of
the bitline for driving with and without preemphasis respectively.
If no preemphasis, the bitline may need several RC time constants
to settle in a normal RC fashion. With optimized preemphasis, the
bitline could settle in half the normal settling time. The voltage
dV1 and the time t1 are determined based on characteristic of the
effective bitline RC loading. These can be trimmed by electrical
fuses (not shown) to optimize memory array organization. The
bitline sensing load circuit 2600 uses charge precompensation to
achieve equalization of the bitline (e.g., a RC line) in a shorter
period of time. Similarly, this preemphasis bitline driving
technique may be adapted to realize preemphasis wordline driving in
the x-decoders of FIGS. 2,3,13, and 16. Similarly the preemphasis
technique may be adapted to realize I/O buffer (IOBUF) driving for
a particular system loading (IOBUF circuitry is part of the I/O
Interface 196). In this case IOBUF circuitry can be configured by
the logic controller 162 or by the microcontroller 20 to realize a
particular preemphasis (dV1 and t1) depending on the
characteristics (R,C,L) of the system and chip packaging loading
that is driven by the IOBUF circuitry.
[0083] In one methodology, a memory operation is controlled for a
memory, such as a Flash memory, by applying a preemphasis signal on
a signal line coupled to the memory cells. In one embodiment, the
preemphasis signal has at least one characteristic dependent on
loading of the signal line. A memory operation, such as read or
write, or a deselection of a group of memory cells, may then be
performed.
[0084] In one embodiment, the preemphasis signal drives a voltage
on the bit line to a negative voltage level for deselection of at
least one of the memory cells. In another embodiment, the
preemphasis signal drives a voltage on the signal line that is less
than a forward bias pn junction voltage.
[0085] The biasing of the bulk voltages, parasitic bipolar action,
preemphasis, and other methods and apparatus described above for a
PMOS transistor may be similarly applied to an NMOS transistor, and
similarly those described above for an NMOS transistor may be
applied for a PMOS transistor. The techniques and schemes for a
well driving and bias as described above may be used for other
portions of the micro controller memory system 100 or the type
memory system 100 such as the high voltage regulation, timing,
bandgap references, I/O buffering described above.
[0086] The body voltage described above may be driven to forward
bias pn junctions in the MOS transistors or to reverse bias pn
junctions in the MOS transistors or combinations thereof. For
example, the voltage on an n-well of a PMOS transistor higher than
the source voltage of the PMOS transistor, for example, to reduce
leakage current. In one embodiment, the local selective bulk
voltage is realized as a chip function or performance (such as
speed). For example in one embodiment, an n-well bulk voltage of
the sensing, wordline and bitline decoding, and IO circuitry is
driven higher than Vdd in erase or program operation to reverse
bias the sensing, decoding, and IO PMOS transistors during program
and erase to reduce, leakage because the sensing function or fast
speed transistor is not used during these operations. In another
embodiment, an n-well bulk voltage of the HV (high voltage) control
circuitry is driven higher than Vdd in read operation to reverse
bias the HV control PMOS transistors during read to reduce leakage
since the HV function is not used during this operation. In another
embodiment, n-well bulk voltage of the sensing, wordline and
bitline decoding, IO circuitry is driven same as the supply voltage
Vdd for medium or slow speed or for higher power supply Vdd level
(such at the beginning of the battery operation, at the end the Vdd
level is typically lowered). Similarly bulk voltage for NMOS can be
realized as a function or performance of chip.
[0087] In another embodiment, the body voltage may be driven to
reverse-bias or forward bias to modulate the threshold voltage Vt
to be higher or lower, so as to increase the input common mode
range of an NMOS input pair of a differential amplifier, such as
the differential amplifiers 2100, 2200 and 2300, or an operational
amplifier (op amp). This is done for example, as the input common
range level is at the low level, the threshold voltage Vt of an
NMOS input pair is modulated to be lowered (accordingly, the NMOS
input pair is turned on because the threshold voltage Vt is lower).
As the input common range level is at the high level, the threshold
voltage Vt of NMOS input pair is modulated to be higher
(accordingly the NMOS input pair is kept in saturation region at
high level because it is harder to put it into linear region since
the threshold voltage Vt is higher). As the input common range
level is at the high level, the threshold voltage Vt of the PMOS
transistor can be modulated to be lowered to increase the headroom
voltage higher for the drain side of the NMOS input pair. The end
effect is that the differential amplifiers or the op amp have a
more effective input common mode range.
[0088] The tracking bias voltage generators may be local to the MOS
transistors that include a bulk coupled to the tracking bias
voltage generators. For example, the decoders 304 and/or word line
drivers 306 may include the tracking bias voltage generators. As an
illustrative example, a tracking bias voltage generator is local to
the MOS transistor, such as the tracking p-region load body bias
circuit of the differential amplifier 2200. As an another
illustrative example, each of a plurality of voltage generators 400
is local to a corresponding one of the PMOS transistors 361, each
of another plurality of voltage generators 400 is local to a
corresponding one of the PMOS transistors 371. In another
embodiment, the tracking bias voltage generators are physically
local to the corresponding MOS transistors in the integrated
circuit. As an illustrative example, the tracking p-region load
body bias circuit of the differential amplifier 2200 is adjacent
the PMOS transistor 2202.
[0089] In the foregoing description, various methods and apparatus,
and specific embodiments are described. However, it should be
obvious to one conversant in the art, various alternatives,
modifications, and changes may be possible without departing from
the spirit and the scope of the invention which is defined by the
metes and bounds of the appended claims.
* * * * *